//黑白效果
precision mediump float;
uniform sampler2D vTexture;
varying vec2 aCoord;
void main() {
  vec4 tempColor = texture2D(vTexture,aCoord);
    float luminace = tempColor.r * 0.299 + tempColor.g * 0.584 +tempColor.b * 0.114;
    gl_FragColor = vec4(vec3(luminace),tempColor.a);
}
